This invention pertains to the electronic compensation of the existing micro-speakers contained in earphones or earbud headsets. The compensation is designed to modify the normal micro-speaker output as a function of acoustic frequency so as to: (1) produce a desired response that can compensate for the hearing deficiency of users, usually elderly, that suffer from presbycusus, or age-related hearing loss, which is characterized by a hearing loss that becomes more severe as the acoustic frequency moves to higher tones. Other chosen frequency characteristics can be similarly provided.
A micro speaker is significantly different from “the generally known speaker” as shown in U.S. Pat. No. 6,553,126 by Han et. al (2003). He describes the generally known speaker in (col. 1, ln. 14-20). The “conventional micro speaker” is described in (col. 1, ln. 29-col. 2 ln. 6).
He notes, for example, that the magnet of the “known speaker” has the shape of a thick washer that is connected on both faces by the yoke and the upper plate. The vibrating element has the shape of a cone. On the other hand, for the micro speaker, the magnet is a simple disk, and the upper plate is a similar flat disk. The vibrating element is a membrane that completely covers and is suspended slightly above the upper plate. By using a vibrating element that is very thin and light, a relatively high resonance frequency response is obtained. Additionally, micro speakers are known by their quite small size, being in the range of 14 mm diameter to 9 mm diameter or slightly smaller. The smaller sizes with rare earth magnets have higher frequency resonant response peaks.
U.S. Pat. No. 7,505,603 by Yoo (2009), similarly differentiates between general speakers, combinations of speakers, and micro speakers. Again the main differences are the small size and the design layout for the micro speakers.
U.S. Pat. No. 6,804,368 by Tsuda (2004), describes a method of using a low volatile magnetic fluid as a damping mechanism for a micro speaker. He points out the differentiation between the micro speaker and conventional audio speaker.
The micro-speakers being addressed in this disclosure are those contained in earbuds/earphones used with personal audio devices such as I-Pods, MP3 players, etc. These micro-speakers usually have a diameter of 9 mm to 14 mm and their acoustic frequency characteristic is characterized by a maximum in the response that is in the range of 2000 Hz to 4000 Hz. The micro-speaker response declines for all micro-speakers at frequencies both higher and lower than the maximum by as much as 25 dB at 300 Hz and 25 dB at 10,000 Hz.
Considerable effort has been expended by various manufacturers to improve the earbud/earphone frequency-response. This work has resulted in devices that show smaller reductions in response at both high and low frequencies while at the same time moving the peak response of the micro-speaker to higher frequencies (as high as 4000 Hz.). All these efforts have concentrated on mechanical approaches. As the response curve becomes flatter the price of the earbuds increases, sometimes to several hundreds of dollars. Parenthetically, the cheap end of the earbud market is at about one dollar.
US2007/0258598 describes a method of characterizing the parameters of a micro-speaker (i.e., the frequency output characteristics). Those parameters describe the functionality of the micro-speaker itself but do not address methods of significantly changing or improving the basic micro-speaker properties. This application details how an existing earbud/earphone system's parameters (not otherwise defined) can be changed/modified by using an algorithm to select a designated parameter of the micro-speaker and optimize it by the change in other different parameters. An example is given in FIG. 5 of this application in which the sharp spikes in the frequency spectrum of a micro-speaker are suppressed by this parameter optimization method. The sharp spikes are probably due to high order mechanical coupling effects. No effort is made to modify the fundamental response spectrum of the micro-speaker.
USPAP US2006/0140418 shows a method of compensating the frequency of an acoustic system. It uses digital signal processing and it relates to the “jazz”, “modern rock”, etc. modes of changing the output of a portable sound system (not otherwise defined). It also discusses the possibility of modifying the “acoustic characteristics of a user” by use of a computer-audio generator-headphone system. This fitting to a specific user does not reflect the mode of modification or the intent of this disclosure.
U.S. Pat. No. 7,184,556 by Johnson et. al. (2007). Due to these significant differences noted above, one cannot justifiably apply analyses and corrective measures that are proposed for “generally known speakers” to an analysis and corrective measures for micro speakers. In Johnson, et. al. the concept of the invention is to model a speaker and its environment with a series of realizable filters and delay modules. Most of the specifications focus on defining the problems and discussing the model. Although the concept of utilizing a “conjugate” is mentioned 44 times throughout the patent, the means by which it is addressed is in the most vague and general terms, such as that it is done by a “controller” and that a “computer” can be used. In fact, Johnson really teaches nothing that is useful in actually fabricating a useable system.
US2007/0098186 describes a “tone control” for a hearing aid, sound equipment and the like. The figures in this reference are typical audio amplifier tone controls (i.e., a type of “graphic equalizer”). No mention is made, nor is there discussion of the effects of the non-uniform properties of the micro-speaker of a hearing aid or how such non-uniform response is to be corrected.
U.S. Pat. No. 3,927,279 shows a method of tailoring the electronic design of a series of amplifiers and filters to modify the output spectrum of a hearing aid. The data, shown as FIG. 6, show a maximum gain of about 25 db from 300 Hz to 1500 Hz for a control voltage of 0.9 volts. Both the spectrum and the maximum gain shown are consistent with an uncorrected micro-speaker with a battery voltage of about 1 volt. The maximum overall gain is reduced as the battery voltage is reduced due to drain on the battery that lowers the nominal voltage. No mention is made of methods for extending the amplifier output to useful values at higher frequencies (above 3000 Hz).
U.S. Pat. No. 5,475,759 speaks to the reduction of the feedback problem that causes an aggravating squeal when the gain is advanced to a very high value. A filter system is used to address the problem by utilizing two channels from an input and using one of them to provide an adaptive method to suppress the unwanted feedback component. Again, no discussion is offered concerning the response of the micro-speaker to acoustic signals of differing frequencies.
U.S. Pat. No. 4,926,139 uses a set of 4 pole filters that have a 24 db/octave filter roll off, together with an ACG circuit to tailor the resultant output to match the hearing deficiency of individual hearing aid users. This approach uses DSP components and sophisticated logic for its purpose. This patent does not address changing the spectrum of a micro-speaker.
U.S. Pat. Nos. 5,663,727, 7,466,829, 7,433,481, 4,792,977, and 4,887,229 are directed to digital hearing aids and methods used to improve the fit to individual users. None of them discuss correcting the micro-speaker response spectrum.